1. Field of the Invention
The present invention relates to a check valve for passing a flow only in a predetermined direction, for use in, for example, a secondary air supply system for an internal combustion engine.
2. Description of the Related Art
In the prior art, there are well-known check valves of this type including a reed valve utilizing the elastic force of a metallic thin plate called a reed, and a disc valve utilizing the elastic force of a disc-like rubber plate.
FIGS. 11 and 12 are sectional views showing a structure of a conventional disc-like check valve of the latter type. FIG. 11 shows a closed state of a valve element, and FIG. 12 shows an opened state of the valve element. In the drawing, reference numeral 1 designates the valve element, 2 is a spring, 3 is a valve seat, 4 is a stopper, 5 is an upstream hollow case, 6 is a downstream hollow case, 30 is a communicating hole, 40 is a caulked fixing portion, and 50 and 60 are respectively opening portions in the upstream hollow case 5 and in the downstream hollow case 6.
The valve element 1 includes an elastic material such as a rubber plate, and is pressured by the spring 2 disposed downstream of the valve element 1 in a direction to block the communicating holes 30 provided in the valve seat 3. The stopper 4 is fixed by the caulked fixing portion 40 at an intermediate portion of the valve seat 3 through the valve element 1 and the spring 2 so as to hold the valve element 1 and the spring 2. Further, an outer edge of the valve seat 3 is clamped and fixed between the upstream hollow case 5 including the opening portion 50 serving as an inlet for fluid, and the downstream hollow case 6 including the opening portion 60 serving as an outlet for the fluid.
A description will now be given of the operation. When fluid is supplied upstream of the check valve, fluid pressure is applied to the valve element 1 which is blocking the communicating holes 30 in the valve seat 3. As a flow rate of the fluid more increases, the amount of deformation of both the valve element 1 and the spring 2 increases, thereby passing the fluid introduced through the opening portion 50 in the upstream hollow case 5 toward the opening portion 60 in the downstream hollow case 6.
In this case, in the check valve, as the fluid pressure becomes higher, the amount of deformation of both the valve element 1 and the spring 2 increases to pass a large amount of fluid. However, the amount of deformation is limited by the stopper 4.
When a difference in internal pressure between the upstream hollow case 5 and the downstream hollow case 6 is equal to zero or small, the valve element 1 is pressed by the elastic force of the spring 2 onto the valve seat 3, resulting in a closed state.
Further, the fluid pressure may be applied in a direction opposite to a regular flowing direction, i.e., toward the upstream from the downstream hollow case 6. In such a case, since the valve element 1 receives the fluid pressure in addition to its restoring force and the pressing force of the spring 2, the blocking force of the valve element 1 increases to prevent counter flow of the fluid.
The conventional check valve is provided as set forth above. Therefore, though smaller flowing resistance and a more effective function against counter flow have been desired, the rubber valve element 1 and the spring 2 are elastically deformed by the fluid pressure in the check valve shown in FIGS. 11 and 12. That is, there is a natural problem in that the resistance to flow becomes greater. Alternatively, in order to overcome the problem, there is an available method in which the valve element 1 can easily be deformed. This method of approach, however, reduces the pressure resistance of the valve element 1 to counter flow pressure, resulting in reduced reliability of the check valve. The check valve of the prior art is disclosed in, for example, Japanese Utility Model Publication (Kokai) No. 56-67466, or Japanese Patent Publication (Kokai) No. 50-27121.